What is the greatest common factor of $20$ and $28$ ? Another way to say this is: $\operatorname{gcf}(20, 28) = {?}$
The greatest common factor is the largest number that is a factor of both $20$ and $28$ The factors of $20$ are $1$ $2$ $4$ $5$ $10$ , and $20$ The factors of $28$ are $1$ $2$ $4$ $7$ $14$ , and $28$ Thus, the greatest common factor of $20$ and $28$ is $4$. $\operatorname{gcf}(20, 28) = 4$